Ventilation duct structure for a wood waste burner

ABSTRACT

A duct structure centrally disposed below a wood waste burner providing combustion supporting air to the interior of a waste pile formed within the burner interior. A central main plenum and a supply conduit therefor are in tangential communication to provide a circular, upward flow of air through intake and exhaust zones of the plenum. Secondary plenums are located outwardly from the main plenum at the ends of lateral conduits which are in upstream communication with the exhaust zone of the main plenum. Air flow within each of the secondary plenums is in a circular, upward direction and ultimately discharged vertically, upwardly in a forceful manner into the base of the waste pile. A blower assembly, exterior of the burner structure, provides a burner temperature regulated flow of pressurized air to the main plenum.

United States atent 1 Stutz 1 May 8, 1973 [54] VENTILATION DUCT STRUCTURE Primary ExaminerKenneth W. Sprague FOR A WOOD WASTE BURNER Attorney-James D. Givnan, Jr.

[76] Inventor: John D. Stutz 96 E. Hatton Ave.,

Eugene, [57] ABSTRACT [22] Filed: Manzo, 1972 A duct structure centrally disposed below a wood Appl. No.: 236,036

waste burner providing combustion supporting air to the interior of a waste pile formed within the burner interior. A central main plenum and a supply conduit therefor are in tangential communication to provide a circular, upward flow of air through intake and exhaust zones of the plenum. Secondary plenums are located outwardly from the main plenum at the ends of lateral conduits which are in upstream communication with the exhaust zone of the main plenum. Air flow within each of the secondary plenums is in a circular, upward direction and ultimately discharged vertically, upwardly in a forceful manner into the base of the waste pile. A blower assembly, exterior of the burner structure, provides a burner temperature regulated flow of pressurized air to the main plenum.

6 Claims, 5 Drawing Figures VENTILATION DUCT STRUCTURE FOR A WOOD WASTE BURNER BACKGROUND OF THE INVENTION The present invention relates generally to wood waste burners and particularly to a duct structure directing a pressurized flow of air to the base of a wood waste pile within the burner for optimum combustion.

Typically, wood waste burners are located adjacent various types of wood working plants i.e., veneer mills, plywood mills, sawmills and the like. The wood waste from the plant is continuously fed by a conveyor into the upper end of the burner structure whereupon it is discharged onto a burning pile several feet in height. Such burners are characteristically of conical shape having a rounded or domed upper end formed of wire mesh. Burner size may vary depending upon the size of the plant and the volume of waste wood therefrom with circular base dimensions running between to 100 feet (approximately) and with burner height being somewhat greater than its base dimension. Such burners are sheathed with sheet metal and define an unobstructed interior area within which the waste pile is formed.

For many years burner operation has entailed simply the depositing of the wood waste therewithin with ventilation of the burner fire being in a more or less haphazard manner. Usually a plurality of air vents were formed immediately above the burner base with air passage through said vents being regulated by manually positionable damper plates. While such burner structure and operation was adequate from the standpoint of disposing wood waste, it did not provide for efficient, low emission combustion. Accordingly, burner operation resulted in objectionable high particle and smoke emissions into the atmosphere. Additionally, the inefficient and slow burning of wood waste required a burner structure of considerable size and hence substantial cost. I

Public concern over air quality has resulted in far reaching and strict emission limits being enacted by several states with burner operation in the Western part of the United States being subject to individual state as well as federal restrictions. Operation of such burners in violation of state regulations subjects the mill owners to fines and in cases of repeated offenses, enjoinment of further burner operation.

SUMMARY OF THE PRESENT INVENTION The present burner duct structure is located subjacent the burner base for the discharge of pressurized air streams evenly and upwardly into the waste wood pile.

Important to the present duct structure is a centrally located main plenum provided a continuous, tangential flow of pressurized air from a source exterior of the burner and which source may be regulated in accordance with internal burner temperatures. Secondary plenums, located outwardly about the main plenum, receive a cyclonic flow of air which ultimately passes upwardly through a plenum grate into the waste pile for uniform dispersion into the pile. The secondary plenums are desirably disposed in an alternating manner adjacent and remote from the main plenum with their distance as well as number being determined by the size of the burner and the normal diameter of the waste pile burned therein.

Supplying the duct system is a blower assembly. During starting and normal operation a full flow of air is admitted to the base of the waste pile while elevated burner temperatures warrant a reduction in the air flow to avoid excessive, burner damaging temperatures.

An important object of the present duct structure is to adequately provide combustion supporting air to the base of a waste wood pile within a burner structure. Air, so provided, encounters a minimum of frictional resistance to efficiently derive full benefit of the blower output. Irnportantly, undesired directionalizing of the discharged air is avoided. The latter concerns the tendency of an-air flow to retain its original horizontal course which in the present instance is along a horizontal vector. The present duct structure directs the air through a main plenum wherein the flow is initially elevated and dispersed and finally discharged through secondary plenums which exhaust the air upwardly, perpendicular to its original horizontal direction. The above is achieved without undue air flow resistance or undesired air flow turbulence.

A further object of the present duct system is the provision of a main plenum in combination with a secondary plenum the latter partaking of the cyclonic flow of the main plenum and discharging air centrally of the main plenum.

A still further advantage of the present duct structure resides in secondary plenums which include a grate member spaced upwardly from its plenum to provide an air space through which air may be discharged into the pile base even though the grate openings are temporarily blocked by burning wood.

BRIEF DESCRIPTION OF THE DRAWING In the accompanying drawing:

FIG. 1 is a side elevational view of a burner structure with the present duct structure installed in place therebelow,

FIG. 1A is a plan view taken along line 1A-1A of FIG. 1 of the blower assembly of the present duct structure,

FIG. 2 is a plan view of one embodiment of the instant duct structure taken along line 2-2 of FIG. 1 and shown independent of the burner structure,

FIG. 3 is a side elevational view of the main plenum taken along line 33 of FIG. 2 with the laterals removed from said plenum, and

FIG. 4 is a side elevational view taken along line 44 of FIG. 2 of a typical secondary plenum.

DESCRIPTION OF THE PREFERRED EMBODIMENT With continuing reference to the accompanying drawing wherein applied reference numerals indicate parts similarly identified in the following specification the reference numeral 1 indicates generally a typical wood waste burner located adjacent a wood working mill of one type or another. A domed upper end 2 of the burner may be of wire mesh, and in accordance with recent burner modifications, not a part of the present invention, may include damper doors positionable in response to burner temperatures. One such damper door arrangement is shown in a copending US. patent application entitled Control System For A WoodWaste Burner filed Feb. 28, 1972.

A waste pile is indicated at WP onto which wood waste is gravitationally deposited by a conveyor 3 having an onloading end portion receiving wood waste from various mill operations. Normally a mound of waste wood is formed prior to ignition of the waste at the start of a work day with the fire being fed more or less continuously by deposit of waste onto the pile.

With regard to the present duct system the same is indicated generally at 10, shown in FIG. 1 installed in place adjacent the base of the burner structure 1. While a burner base at 1A is shown to be of slab construction, the supporting surface for the pile may instead be a level ground surface without affecting the instant invention.

,With reference jointly to FIGS. l and 1A a source of pressurized air in the form of a blower assembly generally indicated at 11 which feeds a buried main supply conduit 12 extending approximately to the center of the burner base 1A. Conduit 1 .2 is in communication with blower assembly 11 via a square to round adapter section 13. A centrifugal fan housing at 14 is fitted with an inlet housing 15 within which a damper plate 16 is pivotally mounted. The damper plate is positionable from a partially closed position (shown in FIG. 1A) to a full open position by means of an air cylinder 17 and its rod member 17A. An arm at 18 comprises the damper operating linkage. A solenoid actuated, four-way air valve at 20 constitutes control means for said cylinder and directs cylinder actuating air via' lines 21-22 alternately to opposite ends of the cylinder for rod movement for positioning of the damper 16.

Electrical signals into the solenoid operated valve via electrical leads 23-24 originate within temperature actuated switch means not part of the instant invention. By way of explanation only, such temperature actuated switch means may be part of a temperature recording instrument responsive to thermocouple sensed temperatures within the burner structure. The aforementioned copending application describes one such electrical control system for burner accessory equipment.

With attention to FIGS. 1 through 3, the main plenum is indicated at 25 and is of cylindrical configuv ration having a tangentially located inlet at 26 in its lower portion for reception of an air flow from conduit 12. The plenum is closed by bottom and top walls 27 and 28 with the top wall receiving a centrally located secondary plenum 30 medially disposed therein as seen in FIG. 3. Formed within the upper peripheral wall of the main plenum are a series of openings 25A all for registration with outwardly extending lateral conduits 31-32 removed from the plenum in FIG. 3. The laterals are disposed in alternating fashion with the shorter conduits 32 interposed between longer conduits 31.

The main plenum 25 is divided into a lower intake zone 12 and a superimposed exhaust zone E2 the zones associated respectively with an incoming air flow from conduit 12 and with a discharge air flow out laterals 31-32. Air entering the intake zone follows the curved plenum wall into a circular flow pattern with an upward component as shown in FIG. 3. The circular air flow eventually enters the exhaust zone EZ from which it passes outwardly into the lateral conduits 31-32.

The aforementioned secondary plenum 30 has a lower end 30A, disposed within the main plenum 25, which end is fitted with an intake 33 tangentially orientated to secondary plenum 30 and providing a tangentially directed flow thereto. The outer end 33A of the intake segment is located so as to intercept circularly flowing air within the main plenum exhaust zone seen in FIG. 2. Air received by the secondary plenum 30 is discharged upwardly through openings in a grate 34 into the approximate center of the waste pile.

The cyclonic flow of air within the exhaust zone of the main plenum 25 is evenly apportioned to laterals 311-32. Air moving along the laterals eventually enters additional secondary plenums at 35 whereupon it again moves a cyclonic flow upwardly past a grate plate 36. The grate plate is flush with the pile supporting surface IA of the burner and discharges air upwardly in multiple streams out openings at 36A in the plate. With attention to FIG. 4 it will be noted the typical grate shown is somewhat elevated, by means of spacer elements 37, from the upper rim of its secondary plenum 35. Elements 37 are spaced about and welded to the underside of the grate with each element inset at 37A for inset engagement with the plenum wall. Importantly, an annular air space 39 is provided (threefourths inch or so) b elow the grate rim for passage of pressurized air. In instances where the grate openings 36A are blocked by large pieces of wood waste the air is exhausted via said air space 39 into the waste pile. The same is also the case for grate 34 on the first described secondary plenum 30.

Typical embodiments of the present invention include duct structures for various sized burner structures with a desirable arrangement being the locationing of the outermost secondary plenums 35 a few feet inwardly of the typical waste pile perimeter. The size of the burner structure will determine the maximum permissible size of a waste pile which in turn determines the size of the duct structure best suited to tire ventilation. Common sizes range from those having secondary plenums located on six foot centers with the main plenum center to larger duct structures wherein outermost secondary plenums are spaced on eight foot or layer centers from the main plenum.

As regards blower ratings for the various sized duct structures the same may range from 4,500 CFM to 30,000 CFM. A typical supply conduit 12 will have a fourteen inch diameter while a main plenum of 36 by 36 inches has been found highly suitable.

Apreferred mode of operation of the present duct structure entails continuous operation of the blower during operation of the burner with the air flow being regulated by damper 16. During starting of the burner and until burner temperature approaches approximately 900 the damper remains open. Beyond the above temperature, the damper is positioned to the partially closed position by actuation of solenoid valve 20. The reduced airflow now passing through the duct structure serves to prevent excessive temperatures within the duct structure which over a period, would structurally damage same.

While the foregoing description has been rendered with regard to but a typical duct structure it is not intended to restrict the scope of the protection sought as obviously various changes will be readily apparent to those skilled in the art to suit specific installations with such changes coming within the scope of the invention as set forth in the appended claims.

What I desire to secure under a United States Letters Patent is:

l. A duct structure providing a combustion supporting flow of air to the base of a wood waste pile located within a burner structure, said duct structure comprising,

a main plenum centrally located below the burner structure and having an inlet zone and a superimposed outlet zone both defined by a circular plenum wall, said wall of the plenum confining the air therewithin for combined rotational upward movement into said outlet zone,

conduit means in tangential communication with the inlet zone of said main plenum and adapted to receive a pressurized flow of air,

lateral conduits extending outwardly from a main plenum and in receiving communication with the exhaust zone therein, and

secondary plenums of cylindrical configuration in tangential asociation with the outer ends of each of said lateral conduits confining the air for upward movement in a circular manner ultimately discharging same into the base of the waste pile.

2. The duct structure as claimed in claim 1 additionally including a blower assembly located outwardly from the burner structure and providing the pressurized air flow through said conduit means, said assembly including means for regulating the volume of the pressurized air flow.

3. The duct structure as claimed in claim 1 additionally including a secondary plenum integral with said main plenum, the last mentioned secondary plenum having intake means located within the exhaust zone of the main plenum whereby air within the exhaust zone is directed to said last mentioned secondary plenum.

4. The duct structure as claimed in claim 1 wherein said lateral conduits are of at least two different lengths with the different lengths of lateral conduit being arranged in an alternating manner about the main plenum.

5. The duct structure as claimed in claim 1 wherein said secondary plenums each include a grate, means spacing each grate upwardly from its plenum to provide an annular air space for the lateral discharge of an air flow in the event the openings in the grate are temporarily blocked.

6. The duct structure as claimed in claim 2 wherein said regulating means for the blower assembly comprises,

adamper,

damper positioning means, and

control means for said damper positioning means,

said control means in circuit with temperature actuated switch means for positioning of the damper upon predetermined internal burner temperatures being reached. 

1. A duct structure providing a combustion supporting flow of air to the base of a wood waste pile located within a burner structure, said duct structure comprising, a main plenum centrally located below the burner structure and having an inlet zone and a superimposed outlet zone both defined by a circular plenum wall, said wall of the plenum confining the air therewithin for combined rotational upward movement into said outlet zone, conduit means in tangential communication with the inlet zone of said main plenum and adapted to receive a pressurized flow of air, lateral conduits extending outwardly from a main plenum and in receiving communication with the exhaust zone therein, and secondary plenums of cylindrical configuration in tangential asociation with the outer ends of each of said lateral conduits confining the air for upward movement in a circular manner ultimately discharging same into the base of the waste pile.
 2. The duct structure as claimed in claim 1 additionally including a blower assembly located outwardly from the burner structure and providing the pressurized air flow through said conduit means, said assembly including means for regulating the volume of the pressurized air flow.
 3. The duct structure as claimed in claim 1 additionally including a secondary plenum integral with said main plenum, the last mentioned secondary plenum having intake means located within the exhaust zone of the main plenum whereby air within the exhaust zone is directed to said last mentioned secondary plenum.
 4. The duct structure as claimed in claim 1 wherein said lateral conduits are of at least two different lengths with the different lengths of lateral conduit being arranged in an alternating manner about the main plenum.
 5. The duct structure as claimed in claim 1 wherein said secondary plenums each include a grate, means spacing each grate upwardly from its plenum to provide an annular air space for the lateral discharge of an air flow in the event the openings in the grate are temporarily blocked.
 6. The duct structure as claimed in claim 2 wherein said regulating means for the blower assembly comprises, a damper, damper positioning means, and control means for said damper positioning means, said control means in circuit with temperature actuated switch means for positioning of the damper upon pre-determined internal burner temperatures being reached. 